4. Nitrous tuners used to think that running the engine with a rich air/fuel ratio was safer than running it lean. Over the years though, most have come to accept that a rich mixture actually damages more parts than a lean one. The same can be said for running too much ignition timing. The timing advance can be seen on the ground strap. Too much timing and the colored line will appear on the strap near the threaded portion of the plug and that’s a recipe for detonation. If you have way too much timing advance the ground strap can be burned completely off the spark plug. Too little timing and the mark will not be visible or will appear at the very end of the ground strap. On this plug, the rainbow-colored line appears right before the bend, otherwise known as the sweet spot for making horsepower without hurting parts.